Various applications are known wherein a portal requires a closure, or cover, to prevent the passage of wind, rain, light, insects, or any other elements through the portal. As used herein, portal simply means an opening which would allow the passage of such elements therethrough; hence a portal may be a window and the closure of the instant invention may control the passage of any of the above elements therethrough. The present invention addresses the need for improved closures for portals such as may be found on patios, pool houses, green houses, livestock houses, atriums or any other similar structures. The portal may be as small as would accommodate a ventilation fan in a gymnasium or livestock house, or as large as an atrium wall in a solar efficient building or an inclined roof panel. Additionally, the position of the portal can range from vertical to horizontal or any angle therebetween.